In certain types of signal transmission environments, such as communication satellites, it is necessary to couple energy from a plurality of microwave signal sources to a single output waveguide port within the confines of a fixed waveguide system. For this purpose there have been developed various types of variable ratio power combiners which operate essentially as variable directional couplers that provide selective coupling from 0 to 100%. One type of combiner varies the angle of a linearly polarized signal in a circular waveguide with respect to an orthogonal mode transducer (OMT) terminating it, thus varying the coupling between the two output ports from 0 to 100% for either port. This has proven to be an excellent way to combine coherent high power signals, such as multiple transmitters, since the components are usually high power and low loss.
For a system requiring power combining, the two high power signals are combined so that they are in phase at the OMT junction, thus producing linear polarization in the circular waveguide. The angle of polarization is dependent upon the ratio of the powers of the two signals and the linearity of the polarization is dependent upon the phase between the two signals. In any case, the total power of the two signals is established in the circular waveguide.
If the two signals are properly phased prior to entering the OMT, the total power is combined to a single linearly polarized output signal in the circular waveguide. In order to extract that output signal, the output rectangular waveguide must be transitioned to the circular waveguide and oriented to be aligned with the signal for maximum power transfer. This transition in most cases involves the use of another OMT which provides, in its orthogonal port, a null indication of improper phase and/or misalignment. This output OMT may be physically rotated for proper alignment using two rotary joints, but in most cases it is electrically rotated via a 180.degree. differential phase shifter or halfwave plate which is mounted between rotary joints in an arrangement as shown in FIG. 1.
Here, two signals IN1 and IN2 are applied to an OMT 11 via a pair of input ports 10 and 12 that are physically turned 90% from each other. The OMT 11 is coupled to one end of halfwave plate 14 via a rotary joint 13, while the other end of halfwave plate 14 is coupled to another OMT 17 via rotary joint 15. OMT 17 has an output termination at port 16 while the combined signal is derived from port 18. The halfwave plate 14 will cause an impressed linear polarization to rotate at its output port, as it is rotated, and the elliplicity of the output polarization is the same at the output as it was at the input. The phase of the two signal sources IN1 and IN2 at OMT 11 of the variable ratio power combiner are made identical to each other, in order to properly combine the signals over the wide bandwidths of today's transmitters. For exemplary illustrations of microwave power combiners employing the above-described coupling components, attention may be directed to the devices described in the U.S. Pat. Nos. to Bowness 3,094,676, Kolbly 3,588,751 and Rosen 3,668,567.
Now although the above-mentioned conventional coupling schemes provide, in a purely electrical functional sense, the sought-after signal combining of the outputs of a pair of microwave energy sources, their physical configuration leaves much to be desired, since complicated and bulky waveguides runs are required for attachment to the 90.degree.-turned ports of the OMTs. In fact, because of such a configuration, compact housing and symmetrically packaging of microwave source and coupling components is effectively physically impossible.